1. Field of the Invention
The present invention relates to a method for reducing low frequency noise of a transistor operating at cryogenic temperatures, and a reading-out circuit, and particularly, to a method for reducing low frequency noise of transistor operating at cryogenic temperatures, which is allowed to be operable with low noise by illuminating light to the transistor operating at the cryogenic temperatures, and a reading-out circuit.
2. Description of the Related Art
A transistor operating at cryogenic temperatures is used for a reading-out circuit of a cooled highly-sensitive photodetector, and the like, and the noise induced by the reading-out circuit frequently determines a limit of the optical detection. In the present invention, the noise of the reading-out circuit can be reduced, and an extremely-high sensitive photo-detecting technique can be realized.
An active noise reducing method for reducing the transistor operating at the cryogenic temperatures is limited. For example, the following is the noise reducing method which has been previously found by the present inventor. While drain current is flowing in the transistor, the operating temperature is increased up to the temperature at which a noise spectrum is changed, and is again cooled to the original operating temperature. Thereby, the noise can be reduced. Such a transistor operating at the cryogenic temperatures is, for example, disclosed in Japanese Patent No. 3598377.
However, when the transistor, in which the noise needs to be reduced, is included in an integrated circuit, this method brings such a disadvantage that other transistors are also affected by a thermal cycle. For this reason, it is difficult to apply the optimum noise reducing method to each transistor whose gate size and operating condition are different from those of other transistors. Furthermore, since a load to a system is increased by increasing the operating temperature, this method has been able to be applied to limited cases.